In the art of laser engraving a wide range of products are marked including glass, ceramics, steel, plastics, rubber and wood. Various processes are used requiring a wide range of laser beam output properties. Diode only beam outputs usually vary between 1-30 watts power in CW. The beam size is relatively large ranging from 1-4 mm in diameter. The power distribution is usually flat across the spot diameter. Some uses for this type of laser beam with focusing optics include cutting materials or marking materials which are opaque such as wood, rubber, and plastics.
In contrast to the diode laser beam is the diode pumped laser beam whose outputs generally vary from 1-10 watts power continuous wave (cw). The typical Q-switched laser beam size is around 1 mm in diameter. The power distribution is Gaussian having a concentration in the center of the beam. In the Q-switch mode 20 kilowatts or higher of peak power is achieved with 10-30 nanosecond pulses. This type beam is particularly useful for engraving metals.
A brief description of some typical laser engraving applications follows below.
U.S. Pat. No. 4,985,780 (1991) to Garnier et al. discloses a flat bed flying optics laser engraver. Portability is achieved with a first mirror to receive the laser beam and reflect the beam 90.degree.. A second mirror re- directs the laser beam parallel to the laser beam output, and opposite in direction. A third mirror re-directs the laser beam 90.degree.. A fourth mirror re-directs the laser beam downward onto the workpiece. The third and fourth mirrors move with the X-Y carriage assembly. The assembly weighs less then 75 pounds using ball screw and ball nut components.
U.S. Pat. No. 5,523,125 (1996) to Kennedy et al. discloses a laser based mask printing method for marking basketballs, etc. With trademarks. The laser is used to ablate the marking design into a mask before printing over the mask. This is only a printing method. Therefore, no .sctn.103 basis is provided.
U.S. Pat. No. 5,061,341 (1991) to Kildal et al. discloses a printing method to prevent damage to a pigmented plastic article when ink on the article is ablated away by a laser beam. Various coatings of binders and solvents are used. This is only a printing method.
Any laser capable of ablating away the dark coating without ablating away all of the intermediate layer is useful. Highly preferred for such purposes are conventional pulsed lasers that deliver high energy in one or more pulses on a short period of time. Most preferred are those that deliver at least 4 joules per 10.sup.-6 sec over an area of about 1.2 cm.sup.2, such as CO.sub.2 lasers. Convention TEA CO.sub.2 lasers are well-known to be useful for this purpose, for example, as described in the article "Image Micro-machining with TEA CO.sub.2 Lasers", Nelson et al, printed in 1975 in the SME Technical Paper identified as MR75-584. Still other useful lasers that deliver useful energy include pulsed YAG and scanning beam lasers such as continuos CO.sub.2 or Q switched YAG lasers.
U.S. Pat. No. 4,912,298 (1990) to Daniels et al. discloses an ablating process to mark optical lenses. An excimer laser having the energy of the laser beam ranging from 1 to 5 J/CM.sup.2 is used. The mark is more recognizable when the lens has an anti-reflection coating due to the disturbance of the interference condition of reflected light. No chemical processes are taught.
U.S. Pat. No. 4,515,867 (1985) to Bleacher et al. discloses a three step method to mark a glass substrate such as a CRT. First a dark undercoating is applied and dried in under a minute. Second a light colored overcoating is applied in under a minute. Third a laser beam ablates the marking from the light colored overcoating, thus leaving the marking visible as the dark undercoating shines through. The undercoating contains mica particles whereas the overcoating does not. The coatings are made of alkali silicate binder. This is only a printing method.
Another related group of marking methods is a laser combined with glass frit or metal oxide marking mediums. U.S. Pat. No. 4,769,310 (1988) to Gugger et al. teaches first creating a glaze in a kiln process. The glaze has a radiation sensitive additive in amounts ranging from 0.01 to 30% by weight. This glaze is then irradiated by a beam of Nd:YAG pulsed laser having light pulses of six to eight nanoseconds at a wavelength of 0.532 .mu.m and a pulse content of 250 milli-joules.
Energy-rich sources such as lasers are conveniently used to mark the inorganic materials suitable for use in the practice of this invention. The procedure comprises either applying the energy source to the form of the graphic symbols to be applied or focusing it thereon, such that a change in color is induced at the irradiated areas without causing any perceptible damage to the surface of the marked material. Suitable lasers are e.g. those that radiate energy at a wavelength in the near UV range, in the visible range and/or infra-red range.
Examples of such energy sources are solid state pulsed lasers such as ruby lasers or frequency multiplied Nd:YAG lasers, pulsed lasers with booster such as pulsed dye lasers or Raman shifter, and also continuous wave lasers with pulse modifications (Q-Switch, mode locker), for example on the basis of CW Nd:YAG lasers with frequency multiplier or CW ion lasers (Ar, Kr), as well as pulsed metal vapor lasers, for example copper vapor lasers or gold vapor lasers, or high capacity pulsed semi-conductor lasers, and also pulsed gas lasers such as excimers.
Depending on the laser system employed, pulse contents of up to several Joules, intensities of up to 10.sup.12 W/cm.sup.2, pulse durations of up to 10-.sup.15 seconds and frequencies of up to 10.sup.9 Hz are possible. Pulse contents of micro-Joule to Joule, intensities of kilowatt/cm.sup.2 to 100 megawatt/cm.sup.2, pulse durations of microseconds to picoseconds, and frequencies of hertz to 250 megahertz are advantageously used.
It is preferred to use lasers with pulsed light, for example those listed in the following table. Especially preferred lasers are pulsed of pulse-modified, frequency doubled Nd:YAG lasers or metal vapor lasers such as Au- or, in particular, Cu-vapor lasers. Also particularly preferred is a laser beam having a wavelength in the visible and/or near infra-red range. By near infra-red range is meant the range from 0.78 .mu.m to 2 .mu.m.
The following table lists a number of commercially available lasers which may be suitably used in the practice of this invention.
TABLE I ______________________________________ Principal Examples of wavelength commercially (subsidiary available wavelengths) Type/Representative types (mm) ______________________________________ Solid state pulsed lasers ruby laser Lasermetrics 694 (347) (938R6R4L-4 Nd:YAG laser Quanta Ray 1064, (532, (DCR 2A) 355,266) Alexandrite laser Apollo (7562) 730-780 Pulsed lasers with booster such as Raman shifter Quanta Ray UV-IR (RS-1) dye laser Lambda Physik c 300-1000 FL 2062 CW laser with pulse modification Nd:TAG (Q-Switch, 2w) Lasermetrics 532 (9560QTG) argon (mode-locked) Spectra- 514.5 Physics pulsed metal vapor laser Cu vapor laser Plasma- Kinetics 751 510, 578 Au vapor laser Plasma- 628 kinetics Mn vapor laser Oxford 534, 1290 Pb vapor laser Laser CU 25 723 Semiconductor diode M/A COM c. 905 lasers Type LD 65 Semiconductor diode STANTEL lasers Array Type LF 100 c. 905 Pulsed gas lasers (excimer) XeCl Lambda Physik 308 XeF EMG-103 351 N.sub.2 337 CO.sub.2 LSI laser 9000-11000 Science inc., PRF 150 G ______________________________________
In the practice of this invention, the laser employed will be for example a pulsed, frequency doubled Nd:YAG laser with a pulse content from 0.01 to 1 joule/cm.sup.2 a maximum capacity of about 40 megawatts, pulse duration of 6-8 nanoseconds and a frequency of 20 Hz (Quanta Ray DCR-2A, available from Spectra Physics, Mountain View, Calif.).
If a copper vapor laser (Plasma Kinetics 151) is used, exposure will be carried out with a pulse content of e.g. 250 milli-Joules/cm.sup.2, a maximum capacity of about 10 kW, a pulse duration of 30 nanoseconds and a frequency of 6 kHz.
Lasers whose parameters can be readily adjusted, for example pulse content and pulse duration, permit the best possible adaptation to the requirements of the materials to be marked.
The best wavelength to be selected for radiation is that at which the additive effecting a change in color absorbs light most strongly and the inorganic material least strongly.
Three different methods are suitable for laser marking in the practice of this invention: the mask method, the linear marking method and the point matrix method. In these last two mentioned methods (dynamic focusing), the laser is preferably combined with a laser marking system so that the inorganic material can be marked with any, e.g. computer-programmed, digits, letters and special symbols at the point where the laser beam strikes.
The choice of laser system in respect of capacity and frequency depends basically on the marking method employed. The high capacity and low frequency of the solid state pulsed lasers are preferred for mask exposure. The average to low capacities and rapid frequencies of pulsed metal vapor lasers or of continuous wave lasers with pulse modifications are preferred for producing markings that require dynamic focusing. Beam deflection can be effected e.g. acousto-optically, holographically, with galvo-mirrors or polygon scanners, Dynamic focusing makes possible an extremely flexible marking, as the marks can be produced electronically.
U.S. Pat. No. 5,543,269 (1996) to Chatterjee et al. discloses providing a ceramic surface with an image made of a color difference using Airconia and a dopant. The colored area is indicated with a laser beam to reduce the doped airconium oxide to produce an image. This reference is a highly specialized laser/chemical process limited to the use of special ceramics. It does not teach marking of glass, metals and plastics.
The laser used for transferring the image onto the zirconia surfaces was a Nd:YAG laser, Q-switched, optically pumped with a drypton arc lamp. The wavelength of such a laser is approximately 1.06.times.10.sup.-6 meters or 1.06 .mu.m. The spot size of such a laser is approximately 100 .mu.m in TEM.sub.oo (low order mode). The spot size can be increased to 300 .mu.m in MM (multimode) using a 163 mm focusing lens. The spot sizes of such lasers can be made a small as 5 .mu.m by using appropriate lenses. However, it should be kept in mind that laser spot size is a function of the laser-material interaction. The laser spot size depends on the laser wavelength and the lens optics. Thus, the ultimate dot density is determined by the laser and material.
The following parameters were used in the writing and image transfer of a laser onto a sintered ceramic surface of zirconia:
Laser Power: CW average--2 to 40 watts Peak Power--50 W to 5 kW (Q-switched) PA1 Pulse Rate: Up to 50 kHz PA1 Pulse Width: 100 to 150 ns PA1 Sean Field: 114.3.times.114.3 mm PA1 Scan Velocity: Up to 3 meters/second PA1 Repeatability: +25 .mu.m PA1 Wave Length: 10.6 .mu.m PA1 Peak Power: 300 watts--operated at 20% duty cycle PA1 Average Poser: 70 watts PA1 Beam Size: 500 .mu.m and the beam width was pulse modulated
The laser photo marking procedure used in the present invention is described below:
The marking system accepts only vector coordinate instructions and these instructions are fed into the system in the form of a plot file. The plot files are loaded directly into the scanner driver electronics. The electronically stored photographic images are converted to a vector format using a number of commercially available software packages (3.g., Corel Draw, Envision-It by Envision Solutions technology, CA). In the working example of this invention the images were captured electronically with a digital flat bed scanner or a Kodak photo CD. The captured images were converted to the appropriate dot density of approximately 600 dots/cm. These images were then reduced to two colors by dithering to half tones. A raster to vector conversion operation was then executed on the half toned images. The converted vector files in the form of plot files were saved and were laser scanned onto the ceramic surfaces.
The laser written images can easily be erased from the zirconia surfaces by either heating the surfaces in air to around 200.degree. C. For about 10 minutes or by treating with a CO.sub.2 laser operating with the following parameters:
U.S. Pat. No. 5,075,195 (1991) to Babler et al. discloses the use of a special substrate of plastic having an additive of molybdenum disulfide. The special substrate is irradiated with a laser beam to change the light reflectance of the substrate and form a marking.
Examples of such energy source are solid state pulsed lasers such as ruby lasers or frequency multiplied Nd:YAG lasers, pulsed lasers with booster such as pulsed dye lasers or Raman shifter, and also continuous wave lasers with pulse modifications (Q-switch, mode locker), for example on the basis of CW Nd: YAG lasers with frequency multiplier, or CW ion lasers (Ar, Kr), as well as pulsed metal vapor lasers, for example copper vapor lasers or gold vapor lasers, or high capacity pulsed semi-conductor lasers which emit visible light by frequency doubling, and also pulsed gas lasers such as excimer and nitrogen lasers.
Depending on the laser system employed, pulse contents of up to several Joules per cm.sup.2, intensities of up to 10.sup.12 W/cm.sup.2, pulse durations of from 10.sup.-15 seconds to 10.sup.-6 seconds and frequencies of up to 10.sup.9 Hz are possible. Pulse contents of micro-Joule to kilo-Joule, intensities of kilowatt/cm.sup.2 to 100 megawatt/cm.sup.2, pulse durations of microseconds to picoseconds, and frequencies of a few hertz to 50 kilohertz are advantageously used.
Preferred lasers are pulsed or pulse-modified, frequency doubled Nd:YAG lasers or metal vapor lasers, as well as excimer lasers.
The following table lists a number of commercially available lasers which may be suitably used in the practice of this invention:
TABLE II ______________________________________ Principal Examples of wavelength commercially (subsidiary available wavelengths) Type/Representative types (mm) ______________________________________ Solid state pulsed lasers ruby laser Lasermetrics 694 (347) (938R6R4L-4 Nd:YAG laser Quanta Ray 1064, (532, (DCR 2A) 355,266) Alexandrite laser Apollo (7562) 730-780 Pulsed lasers with booster such as Raman Shifter Quanta Ray UV-IR (RS-1) dye laser Lambda c 300-1000 FL 2062 Physik 300-1000 CW laser with pulse modification Nd:TAG (Q-Switch, 2w) Lasermetrics 532 (9560QTG) argon (mode-locked) Spectra- 514.5 Physics SP 2030 488 pulsed metal vapor laser Cu vapor laser plasma- 510, 578 Kinetics 751 Au vapor laser plasma- 628 kinetics Mn vapor laser Oxford 534, 1290 Pb vapor laser Laser CU 25 723 Semi-conductor diode M/A COM c. 905 lasers Type LD 65 (402) Semi-conductor diode STANTEL c. 905 lasers Array Type LF 100 (402) Pulsed gas lasers Excimer XeCl Lambda Physik 308 XeF EMG-103 351 N.sub.2 337 ______________________________________
In the practice of this invention, the laser employed will be for example a pulsed, frequency double Nd:YAG laser with a pulse content from 0.05 to 1 Joule/cm.sup.2, a maximum capacity of about 4 kilowatts, pulse durations of 6-8 nanoseconds and a frequency of 30 Hz (Quanta Ray DCR-2A, available from Spectra Physics, Mountain View, Calif.) If a copper vapor laser with focusing optic (Plasma Kinetics 151) is used, exposure will be carried out with a pulse content of, for example, 250 milli-joules/ cm.sup.2, maximum capacity of about 10 kW, a pulse duration of 30 nanoseconds and a frequency of 6 kHz.
Lasers whose parameters can be readily adjusted, for example pulse content and pulse duration, permit the best possible adaptation to the requirements of the materials to be marked.
The best wavelength to be selected for the irradiation is that at which the radiation-sensitive MoS.sub.2 and the optional additional colorant absorbs most strongly, and that at which the plastics material to be marked absorbs little.
Preferably laser light with a wavelength in the near UV and/or visible range and/or near IR range is used, but most preferably with a wavelength in the visible range.
No one single laser is known which can produce all the above variety of beam output properties. The present invention combines two lasers into one portable device. A diode via a bypass path made of mirrors can be chosen to provide a direct beam output. Alternatively the diode output beam can be physically directed by the same mirrors to inject the requisite power into a Nd:YAG laser, Q-switched, and the like, thereby providing a pumped laser output beam. All of the electronics, lasers and housing are enclosed in a portable enclosure.